The proposed studies are designed to investigate the mechanisms of respiratory failure in patients with chronic airway obstruction, with particular emphasis on the muscles of breathing. Our objectives are to gain a better understanding of the action of the chest bellows and the adaptations in muscle function that may occur in the presence of abnormal lung mechanics both in patients who are stable (who will be studied awake and asleep) and in those admitted to the intensive care unit with acute-on-chronic respiratory failure. Studies of respiratory muscle mechanics will be performed by relating simultaneous measurements of esophageal and gastric pressures to displacements of the rib cage and abdome along the lines recently described by Goldman and co-workers, during resting breathing, increased levels of ventilation and maximal staaic maneuvers. We will also attempt to better define the diaphragm's force-length characteristic in the presence of long-standing airway obstruction by relating electrical activity in the diaphragm to measurement of transdiaphragmatic pressure obtained during maneuvers performed at various constant abdominal configurations. Studies of gas exchange during sleep will aid in defining the mechanism of nocturnal hypoxemia in patients with chronic lung disease. Measurements of relative motion of rib cage and abdomen, pleural pressure swings and electrical activity in the respiratory muscles will be related to changes in gas exchange (end-tidal PCo2, ear oximetry) and sleep stage, and will further be related to the patient's responsiveness to chemical stimuli (CO2 hypoxia) when awake. Studies in the intensive care unit will investigate the relative contribution of worsening mechanical abnormalities in the lungs and airways, decreased drive to breathing and muscular problems (fatigue, weakness and incoordination) to the development of acute-on-chronic respiratory failure, and to problems encountered during withdrawal of mechanical ventilatory support.